Gannon R L, Cato M J, Kelley K H, Armstrong D L, Rea M A
Biological Rhythms and Integrative Neurosciences Research Institute, Armstrong Laboratory/CFTO, Brooks AFB, TX 78235, USA.
Brain Res. 1995 Oct 2;694(1-2):264-70. doi: 10.1016/0006-8993(95)00854-j.
The suprachiasmatic nuclei (SCN) at the base of the hypothalamus are known to be the site of the endogenous circadian pacemaker in mammals. The SCN are innervated by the retinohypothalamic tract, which conveys photic information to the SCN. GABA is one of the most abundant neurotransmitters in the SCN, and has been implicated in the modulation of photic responses of the SCN circadian pacemaker. This study sought to examine the effect of GABAergic compounds on optic nerve-evoked SCN field potentials recorded in rat horizontal hypothalamic slices. The GABAA agonist muscimol (10 microM) potentiated SCN field potentials by 23%, while application of the GABAA antagonist bicuculline (10 microM) inhibited SCN field potentials by a similar amount, (22%). Conversely, the GABA, agonist baclofen (1.0 microM) inhibited SCN field potentials by 48%, while the GABAB antagonist phaclofen (0.5 mM) augmented SCN field potentials by 62%. Recordings performed at both day and night times indicate that there were no qualitative day-night differences in GABAergic activity on SCN field potentials. This study concludes that, in general, GABAA activity tends to increase, and GABAB activity tends to decrease the response of SCN neurons to optic nerve stimulation.
已知位于下丘脑底部的视交叉上核（SCN）是哺乳动物内源性昼夜节律起搏器的所在部位。视网膜下丘脑束支配着视交叉上核，该束将光信息传递给视交叉上核。γ-氨基丁酸（GABA）是视交叉上核中含量最为丰富的神经递质之一，并且与视交叉上核昼夜节律起搏器的光反应调节有关。本研究旨在检测GABA能化合物对大鼠下丘脑水平切片中记录的视神经诱发的视交叉上核场电位的影响。GABAA激动剂蝇蕈醇（10微摩尔）使视交叉上核场电位增强了23%，而应用GABAA拮抗剂荷包牡丹碱（10微摩尔）对视交叉上核场电位的抑制幅度与之相似，为22%。相反，GABAB激动剂巴氯芬（1.0微摩尔）对视交叉上核场电位的抑制率为48%，而GABAB拮抗剂法氯芬（0.5毫摩尔）使视交叉上核场电位增强了62%。在白天和夜间进行的记录表明，GABA能活性对视交叉上核场电位没有质的昼夜差异。本研究得出结论，一般来说，GABAA活性倾向于增强，而GABAB活性倾向于降低视交叉上核神经元对视神经刺激的反应。
